Method of and apparatus for investigating subterranean strata



Feb. 25, 1958 G. PETERSON 2,825,044

METHOD oF AND APPARATUS FOR INVESTIGATING SUBTERRANEAN sTRATA Filed Aug. 2, 1949 f 4 sheets-sheet 1 80 mummmm "www l INVENTOR "nhl M Feb. 25, 1958 G. PETERSON 2,825,044

METHOD OF AND APPARATUS F OR INVESTIGATING l SUBTERRANEAN STRATA Fi1ed`Aug. 2. 1949 4 sheets-sheet s OSCILLATOR /64 l AMPLIFIER F/G' a' F/G. /ov

IN VEN TOR.

Feb. v25, 1958 G. PETERSON METHOD oF AND 2,825,044 APPARATUS FOR INVESTIGATING SUBTERRANEAN STRATA Filed Ag. 2. 1949 4 Sheets-Sheet 4 'IN1/EMDR.

lggillg. caliper; surveys, i permeability jllvl'ernents of `radioactivity do; no tgive .reliableinformatiom` "concerning strata even a-short distance fromthe bore hole;

METHQD F AND. APPARATUS FOR INVESTIGAT- ING'SUBTERRANEAN S'IRATA` Glen Peterson, Tulsa, Okla. Application August` 2, 19.49, Serial No. 108,179 27 Claims. (Cl. 340-18)v (Granted under. Title4 35,.U.S.\Code (1952), sec. 266) The invention described'hereinv maybe manufactured and :used `by or for; the, Governmentzfor. governmentpnrposes, ,without the payment to me of any royalties thereon.

This invention relates-to amethodof; andapparatusfr investigatingsubterranean strata, particularly` strata traversed by, a bore hole. This invention further relates to amethody of and apparatus for producing a display', as byy a. cathode; ray tube, and more particularly adisplaywhich-is representative of the characterV andlocation of subterranean strata..

Previousrmethods of investigating subterranean strata have involved the analysis ofv core samples taken from bore, holes, measurement. of4 electrical potentials, both artificially produced and spontaneous, at various levels in abore hole, caliper surveys to determine borei hole diameter, apparatus for determining permeability of adjoining strata,v and devices for measuring, radioactive emission from' subterranean strata. Information has.: also beenobtained by producingjartifcial explosions in thel earth by the detonation ,of explosive chargesin shot holes,- the seismic waves resulting from thedetonation beingv'measured by the useA of seismometersspacedat various :locations yfrom the shot point.v

These systems are-all' inherently incapableof. providing detailed information concerning more than. arelatively4 small regionzof.l thessnbterranean strataof interest.'v Al- Vthough coring enables the exact composition at apar- .',ticularlocation to-beedetermined, it givesno information regarding formations even a shortdistance from the borey hole from. which, the corel is taken. Similarly, electric: studies, andmeas Eurthenpit is not -possibleto determinethe; angle of dip. offformations, or their orientation in azimuth with respect' te .the bore hole .byf theuse of the: prospecting methods just discussed.` The' mapping of subterranean strata; bythe-,use of artilici a1,1 y-P1joduced seismic waves gives more'. accurate,A results vconcerning the location. of, subterranean stra ta ,but information regarding the character of.' thev` formationsis not provided. Although experienced geolf ogistscaninterpret ltheseismographic records with a considerable degree of: accuracy, mistakes f are almost nevit able-particularly-where non-continuousformations', folds, and other disturbances are `presentin the: formationsfbes ingnalyzedz. y

In accordance withvthe'present invention,.the.disad vantages of such systemsr are overcome, by utilizing apfparatus in which a-:pulsed' beam of" radiation, such as ultrasoniczradiation, is' directed againsty the'` formationsA tothe-investigated,` preferably from a4 bore hole which extendsinto the.. strata of'interest. The.waves reflected from the subterraneanI strata are detected, and the time'- interval between the transmission and detection ofthe radiation-is;accurately. measured',l thereby indicating the distance, of4 the .formationt reiiecting =the1f .waves :from` the radiation: source., 'Ehe'. differences, in:4 reection, diiracstion,-scattering;..and..pplarizinggcharacteristicsiofrdilerent.

United States Patent() 2,825,044 Patented Feb. 25, 1958 ice v.formations enable the nature of the formations'to be determined with a high degree ofaccuracy. Where circular scanningl is utilized, that is, where the radiation source is rotated with successivepulses being radiated at predetermined'intervals, the angularl position and angle' of dip of the formationsmay be determined as well as their nature randdistance'from the radiation source. The infor-.- mation obtained may be displayed conveniently upon the screen of a cathode ray tube, andl photographed, if de'- sired, to provide aepermanent record. In this` connection, Il have-'devisednoveLsweep circuits for the cathode ray tube that enable the information obtained to be displayed in perspective. In accordance with the invention; I fur? ther provide'meansv for maintaining the radiation source in' aA xed angular position in a bore hole, and for indicating the angular position of the radiation source so that small deviations in angular positions are indicated, for example, near the screen'of the'cathode ray tube.

It is an object of the invention to providea method of and apparatus for determining the nature andlocation of subterranean strata with a high degree of accuracy.

It' is a-further object to utilize the radiation, reflection, and detection of ultrasonic radiation to investigate the contour and characteristics offsubterranean strata.

lt is a still further object of the invention to display information regarding subterranean'strata in perspective upon the screen of a cathode ray tube.

Itis astill further object to provide apparatus which is reliablein-operation, producesI accurate results, and is of'rugged construction suitablefor` use in the field.

Various other objects, advantages-and" features of the invention will become apparent from the following detailed description, taken in conjunction with theaccom' panying drawings, in which:

Figure l is a View of the radiation source and detector mounted in a borel hole,l together with the hoisting mechamsm;

Figures 2a; 2b, and'2'r,` areviews of modified forms of radiationsources and detectors;

Figure 3 is a blockv diagram of the electrical system;

Figure 4' is'a diagram illustrating the waveforms at" variousparts of the circuitof Figure-3;

Figure 5. is a schematic circuit diagram of `a portion of the esweep' circuit;

Figure- 6 is at schematiecircuit diagram'y off-another por# tion of. the sweep circuit;

Figurei7 is a schematic circuit diagram'of the transmit` receive switch;

Figure'8 isfa` perspective Vi'ewfofthel cathode ray tube" Figurew9` is a view ofarmodiii'ed'- radiation source andt detector;

FigurezlO is a top view of `"the deviation-indicator; Figure 11's a front elevational of :radiatore and detector;

Figure12 isy aviewof a potentiometer"utilizedto producek a linear sweep voltage;

Figure 13- is'a front elevational'view of'a modified 'form' of 1 radiator and detector;

Figure 14 is a View of a crystaliradiator and -detectorassembly;

Figure 15 isa vertical' sectional"vie'w'fof: aemodid calfhoisting'mechanisrn for simplicity, since it forms' nopart 'offthe invention, but inpractice a more elaborate motor drivenhoisting device'is utilized.' The-casing 10";ir`1s cludes various `electrical-- devices' to' be' hereinafter de;`

'viewfof a modified form" scribed which are connected to conductors forming a part 'fcable 12 and these conductors terminate, in the usual manner, at slip rings, not shown, forming a part of hoisting mechanism 13.

The casing has a vertical shaft 15 journalled therein in any suitable manner, and this shaft is driven by a motor 16 which is supplied with power by a pair of the conductors in cable 12. Shaft carries a rotatable reflector and radiation unit 17 together with the rotor coils 18 of a Syncro 19, the stator coils 20 of which are carried by a frame 21 secured to the casing 10. The casing also includes a gyro wheel assembly 23 for preventing' rotation of the casing about its vertical axis.

The retlector andv radiation unit 17 includes a paraas oil which fills the space between reilector 25 and a resilient membrane 28 secured to the peripheral regions of reflector 25. When the elastic body is vibrated in the described manner, ultrasonic waves are set up in the oil or--other liquid within membrane 28, and these waves are focused into a parallel beam by reflector 25, the beam passing, as shown, through membrane 28 and theliquid in bore hole 11 to the formations defining and adjacent to the bore hole. In this connection, it will be noted that membrane 28 should be formed of a material, such as aluminum, which has transmissibility characteristics to ultrasonic waves similar to those of the liquid through which the waves are initially transmitted.

VIn a preferred embodiment of the invention, elastic body 26 is a llat, relatively thick piezo-electric crystal to which current is supplied by metal electrodes secured to opposite faces of the crystal. The oil within membrane 28 prevents a short circuit between the two crystal electrodes. Alternatively, as shown by Figure 2, the elastic body may 'be a rod 30 of magnetostrictive material which is suitably supported at its inner end by a block 31 secured toretlector unit 17, the outer end of the magnetostrictive rod protruding from the center of reflector 25 and terminating at the focus thereof. The rod is vibrated at ultrasonic frequencies by electrical energy supplied thereto by a coil 32, and supersonic waves are radiated in the manner described in connection with Figure 1. It will be noted that the oil-filled membrane 28 is not required in Athis embodiment of the invention, since the coil 32 may be readily sealed so that there is no danger of a. short circuit between the terminals thereof. With certain types of well fluids, however, the use of the oil lled membrane may be desirable to improve the transmissibility characteristics of the media through which the waves. are propagated. Where very low ultrasonic frequencies are used, the waves may be produced by a diaphragm vibrated by passing alternating current through a coil adjacent such diaphragm. I also contemplate that other types of elastic bodies may be utilized, provided that they are capable of vibration at ultrasonic frequencies when electrical energy is supplied thereto. The reflector inay be included as a part of the elastic body by utilizmg a crystal 32a, Figure 2b, of parabolic or other suitable shape, orthe waves may be focused by placing a metal box 32h, Figure 2b, behind the crystal, to form a pocket on an integral member of half wavelengths in thickness.

Although the unit 17 has been described only as a transmitter of ultrasonic waves, it will be apparent that the unit may also function as a receiver. Thus, ultrasonic waves, particularly those reflected from adjoining formatlons, incident upon unit 17 cause mechanical vibrationy of elastic body 26, thereby producing electrical voltages representative of the mechanical vibrations in the conductors attached or coupled to the elastic body.

In accordance with the present embodiment of the invention, a pulse of ultrasonic radiation is periodically produced by vibration of elastic body 26. The resultant ra-- diation beam is directed against the strata at the walls of the bore hole. A portion of the radiation is reflected back toward the unit 17 while another portion is reflected im such a direction that the angle of incidence is equal to the angle of refraction. Still another portion o f the radiation penetrates the str'ata behind the bore hole walls and is reflected wherever a discontinuity exists, such as an intrusion of a different formation, a part of this radiation being reflected back to the unit 17, and the remainder being reflected along other paths or penetrating still further into the adjoining formations. v l l l In Figure 1, the radiation reflected back to the unit 17 is converted into electrical energy, and the time interval between transmission of the original pulse and reception of the rellected wave isV accurately measured, thus accurately determining the distance between the elastic body 26 and the formation from which the energy is receted. The nature of the formation may be accurately determined from the characteristics of the reflected radiation. Theunit 17 is continuously rotated as the successive pulses of radiation are emitted so that an accurate picture is obtained of the entire area surrounding the bore hole. The radiation is of a wave length smaller than the salient features of the strata of interest, and the term ultrasonic radiation is utilized herein to signify elastic waves or vibrations in material media, these waves ordinarily having a frequency' of about 100 kilocycles to l0 megacycles. l tended to signify ore bodies, oil deposits, all types of' rock structures, Water, and the like. A l

In order that an accurate picture or display of the strata of interest may be obtained, rotation of the casing .l0

about its vertical axis must be prevented. To this end, l

have provided a gyro Wheel assembly, a cradle 3d, Figure 1, fixed to casing 10, this cradle having a horizontal shaft 35 journalled therein.

cluding the axis of casing 10 and which is driven at a high rate of speed by a suitable motor, not shown. The

gyro wheel operates in well understood fashion to pref vent rotation of the casing about itsvertical axis.

Despite the provision of gy'ro wheel 36, the angular position of the casing may vary by one or two degrees fnom its predetermined position. it is desirable that this angular deviation be accurately measured and that cor-- recticns be made therefor, where extremely accurate rcsults are desired. -Accordingly, as an optional feature,

I may provide a device for sensing .and recording deviationv of the casing from its predetermined angular position. Such a device is shown by Figure 10, and it may.A be mounted directly above the gyro wheel lassembly of Figure 1, if desired. This unit includes a gyro wheel 38 fixed to a shaft 39 which is journalled in a iloatinlif' position in the casing iii, Figure l. That is, the assembly'-` carrying shaft 39 is free to rotate about the vertical axis of casing lil. The gyro wheel assembly is adapted to rotate about a vertical pin or shaft 40 which is Ilocated at the vertical axis of the casing. A switch 41 is fixed' to the casing and it has a series of contact point-s 42 lall connected to =a common conductor 43 which is connected to one terminal iof a counter 44. Switch 41 has an arm 45 pivoted on a pin 46 which is fixed to the cas tactoi` 47 with the result that a pulse of one polarity is fed "1 0 r:counter '44 eah a contactpoint 42 passesf The term formationsf 'as used herein is in# Shaft 35' has a gyro wheell 36 iixed thereto which is disposed in a vertical plane m-` @assistent ondata onstaat .amata 'Elieaoountert thus t sth lane 111 timoh ioatinaayto wheel? "38. rotates. Qa erdooltwiSerotation-rof.thawing:relative-foam Aeoordinglm, :storting asaafo.. Figure.' 1. the casing,

ismaiiltained.,inaubstantillv xedasulanpostion .bv gyro wheel 36 and'counter 44; Figure 10, continuously., udioatesthe deviation.. of...tl 1o. casing. from.. itsv Predeterminedtangular position. .Y As, stated, while scanner 17` isrotated, -radiationpulses are emitted periodicallyfrom` elasticY body 216,' which, receives reilected. supersonic waves duringgthe, period'sbetween transmissions. The. surface equipment for producingithese. results isv shown by the block ,diagramot Figure.

pulses l`are producedby ,al multivibrator circuit 50,"these pulses .boina illustrated by graph: 51, Figure 4- The squarer wave pulses are differentiatedbyj acircuit 5210,.

Produoefsharg pulses, 5.3, 54 of opposite polarity- The. pu 53, 54" `e rectifred'by unit ,5,6'to produce aser-ies pulses 57jare.: `ed to ahighly dampedoscillator 59 which is, tunedgto. a suitablerultrasonic frequency, spch as 1 messo/cle. Aooordinalueachtime. oscillator 59 isoaoitod, by, a. .pulsa 5L a Short 'pulse of radio frequenor energy isproducedgtby thje oscillator 59; The successive, i'adio'frequency, pulses from oscillator v59 pass through IKI'IIIL.,Switch` v|50L ar'1 d. `Y aftransmission line 61` forming a, partfoffcable `12,1]5`igure l, to reilector 17v and elastic body 26.-' ATR" switchg60 olers a low-impedance to pulsesl produced by-oscillator" 59- but` presents a high impedance, to incoming signals traversing transmission line A61;` s Thusg-,by `the described circuit; a pulsed beam offultrasonic7energy'- ifs-emitted from unit 1'7- eachtime During-tliefperiods between transmissions, reectedultrasonic Waves-"incident upon- `reflector unit 17' cause vibration of elastic body 26'and Vproducega voltage in transmissionyline 631;A vwhich isj representative of the reectedultrasonic-wra-v'es. These voltages pass through TR'v switch 6.3i amplii'er 64; demodulatoror detectorV unitl 65j; and videov a'unplilier166,A the audio frequencyI output olif4 which-fis; utilized-,'- in a-V preferredf embodiment of I theI inventiong to control the-intensity ofi au electronbeam inf-a'tcathode rayftub'e.V InFigure 3','unit 67'represents Aa cathode'rayoscilloscope, thescreen offthe cathode rayv tubebeingdenoted'by referencecharacter 68. In this circuit; TRl switchgolers a lowfimpeda-nce topincoming'A signals received fromy transmissionline-61 and functions toisliqrt circuit the-:input circuits kvofampliiiers 64iwhenv asignaliieproducediby:oscillator 591.

AsI previously stated, scanning-device 17 is-continuouslyrotated-bymotor `16nwhen 'a surveyis being made. The

rotation Iof motor 16 ismechanically-.transmitted to'- syncro'i19- bysh'afLIS, Figure 1, andfsyncro 19 iscon-` nected -by-line 701 forming ay part. of'cable V12, Figure ly to a receiving -syncro-fll. Thus,qthev angularfpositionx off-Syncro. 71' always'corresponds with that'of reflector unit='17'.^ Syncror..71, in a preferred'embodiment of the invention, pnodu-cestwo sinusoidal components 180 degreeseoutoftphase whichnare applied t-o th-e dcection plates of the cathode ray tube 68 to produce a circularV sweep .ofi the .electron .beam at an angular.v velocity equal to-.that-otreflector-unitr17,

f.: Tdmingapulses 57;.Fgure 4.,trom. zoonlief-15.6, are todos` aniRQ-cireuitqzjito.provide aolinear sweepwoltage for.'v thaaoathosletraya tube-rhubarbe wavstorm..showof by..

deviationaof .the -oasinarelative .to

laterali,"4 timiaarulses 57'- In `one channel;v timingv` ilector unit 25'producin-gran electrical voltagewhich is.

grapbt7gligure4, This- Wave d ijfersfron; conventional Saw. tooth wavesused to providelinear sweepvoltages` in, thateach wave has a steep. front 74 which is prof ducedas thewave rises abruptly to a peak value and an exponentially declining substantially linear sloping portion following wave front 74.V The ordinary saw tooth wave risesgradually tro-its peak value and has a sharply tlcclining` yback portion during which, the voltage drops fromitspeakvalue to zero amplitude. Thus, the wave '73 may be described as an invertedsaw tooth wave.

The inverted saw tooth wave from circuit 72 is fedv to la modulator 77 where it is, in efect, multiplied by the sinusoidal voltages produced by syncro 71. The resulting waves are shown by graphs 78 and 79, Figure 4. It will be notedthatwave 78 has a sinusoidal envelope 86, the frequency of, which is determined by the rotation frequency of scanner 17. The inverted saw'tooth voltages Share fitted Within envelope 80 by the modulating unit 77. The time scale of graph 78 is, of course, different from that of the preceding graphs, the duration of waves 81. being equal to the duration of the respective inverted saw, tooth waves 73. Wave. 79 consists of a sinusoidal' envelope 82- which is 90 degrees vout of phase with respect to wave 80, and inverted saw tooth waves within the envelope. When Waves 78, 79 are applied to the, respective sets of detlection plates of a cathode ray tube, a circular sweep of the electr-on beam is produced, the angular velocity ofwhich .is equal to that of reector unit 1,7. Simultaneously with the circular sweep, the electron bearn'fmoves cyclically in a substantially linear lpath between the cen-ter of the circle andl its periphery. Eachv cycle consists of an extremely rapid movement of the beam from center toperiphery of thefcircular sweep pattern followed by a relatively slow movement of the beam from the periphery to the center.

In the, operation of the system as thus yfar described; casingv 10 is lowered int-o a bore hole to they depth ofthe Iformations ofinterest, motor 16 is operated'to rotate scanning mechanism 17, and operation of gyro wheel 36 is initiated to-maintain the casing 10 in a steady angular position. Oscillator 59 is excited by a pulse 57 with the result that -a pulsed beam of ultrasonic radiation is directedv against the formations adjoining the` bore hole -by reflector unit 17. Simultaneously, wave front 74 is'fed' toy the cathode ray tube, causing the electron beam to move to. the periphery of the circular sweep pattern, T R' switch vshort circuitsampliiier 64 while the pulse-isy transmitted so that no signal is fed to the receiving chan-- nel at this time. A portion of the ultrasonic Waves isreected -by formation 85, Figure 1', and returnsv to refedthrough transmissionline 61 to amplifier v64 and the receiver part of 'theapparatus The reflected waves fromregion 86. of formation S5 areflrst to reach unit- 17- since they have the shortest path length. These Waves are. followed 'by reflected waves from regions of formation below. region 8 6, then by reflectionsfrom successively lower regions of formation 87, and finally byrellections from mineral -body 8S, it being understood that a portion of the ultrasonic radiationpenetrates formation -87'and is reflected from mineral body 88.

As the reections are received during the period be tweenltransmissions, the cathode ray beam moves-ata relatively slow rate from periphery to center of the cir-l cular` sweep pattern. The received' voltages produce4 variations in the intensity of the cathode ray beam-and" the distance of the brightspots th-us producedon theL When the nextV timing pulse excites oscillator 59, scanfV ner 17 is displaced through a small angle by.. motor:` 16` and ..the ,cathode ,ray beam. is v displaced through asimilar F angle by the action `of syncros 19, 71 and modulator 77. This next pulse starts anew cycle -of operation, and when scanner `17 is rotated through Ian angle of 360 degrees, the adjoining formations are completely pictured on the screen of the cathode ray tube. It will be noted that the beam produced by scanner 17 is angularly directed with respect to its horizontal plane. This is important, since each point of the bore hole wall-s in the path of the beam is at a different distance from the scanner when the beam is tilted, as described. If the beam were directed hori- Zontally, reflections Ibetween points spaced an equal distance above and below the plane of the beam would be indistinguishable, since they would be an equal dist-ance from the reector.

The display produced by the formations shown in Fig'- ure 1 is pictured in Figure 8. Formation 85 is represented -by the region 90 between elliptical line 91 and the periphery of the circular display. Formation 87 is represented 'by the region 92 bounded by line 91, andv mineral deposit 38 is represented by the region 93 offset from the center Iof the display. The different formations may be readily distinguished from each other and identiiied due to differences in the display produced by the unlike absorption, reflection, and scattering characteristics of the several formations. Where crystalline deposits are encountered, a distinctive display is produced due to the polarization 'of the radiation beam by the crystal lattices. It will be noted that the position of mineral deposit 88 is accurately defined in azimuth, and its distance may be re-adily evaluated by changing the inter- I:

val between transmission and comparing the resulting oscilloscope patterns.

It is a yfeature of the invention that the angle of dip of formations 8S, 87 may be readily determined, this angle being proportional to the difference in length between the major Iand minor axes of the elliptical line 91 defining the boundary between the formations. If the formations are horizontal, line 91 is a circle since all parts of the boundary are the Isame distance from reflector unit 17. If the formation dips, as shown, region 95 of the boundary, Figure 1, is closer to the reflector than region 96. Hence, the bound-ary is shown as an ellipticajl line, the e-ccentricity of the ellipse being proportional to the angle of dip.

It is a further feature of the invention that a perspective view is displayed on the screen of the cathode ray tube. Thus, formation 85, which is closest to the top of the bore hole, appears at the periphery of the display while lower formation 37 appears at the center of the display. The formations would be viewed in perspective in this manner by an observer at the surface looking down the hole. This novel type of display results from application of the inverted sawtooth wave 73, Figure 4, to the cathode ray tube as a linear sweep voltage. When this type of sweep is used, the distance from the periphery of the circular sweep pattern to a point on the display is proportional to distance of the reflecting formation from unit 17. The perspective type display also has the advantage that the largest area near the periphery of the display portrays the formation nearest the radiator, that is, the walls of the bore hole.

The display produced upon the screen 68 of the cathode ray tube may be recorded on motion picture film as a permanent record.y It is preferred that the counter 44 be mounted close to the screen 68 so that it is photographed along with the cathode ray tube display. Thus, the deviation of the casing from its predetermined angular position may be taken into account and appears adjacent the display to which it is applicable. As 'another optional feature, a depth indicator, not shown, may be attached to cable 12, and its indicator may be positioned adjacent screen 68 of the cathode ray tube. In this manner, the depth of the formations portrayed by anyindividual display may be readily noted. A

'The velocity of propagation ofthe ultrasonic waves in jsalient the bore hole' duid is labout 5,000"fee't lper second, and the Lpath length of the waves is in the neighborhood of l to 10 or even 20 feet. Thus, the elapsed time between transmission and reception of the pulses is at a of about 200 microseconds. This allows ample time for the system to' clear itself of each transmitted pulse before a reception period is initiated. Where the system is operated at a frequency of 5 megacycles, the wavelength is approximately 0.012 inch. This enables line structure of the formations to be readily investigated, the upper limit of operating frequency being set by specular redection from mud or other particles in the bore hole. At this wave length, a piezoelectric crystal functions etiiciently as the radiating element, and a highly directional beam may be obtained by the use of parabolic reilector 25.

The circuit details of certain elements of the block diagram of Figure 3 are shown by Figures 5, 6 and 7. The damped oscillator 59, amplifier 64, demodulator 65, and video amplifier 66 are all of conventional construction and need not be described in detail herein. Multivibrator 50 includes two triodes 100 and 101, Figure 5, and is of Y,

the free-running type. The cathodes of both tubes are grounded, and their anodes are connected through the respective voltage dropping resistors 102, 103 to a'positive power supply terminal 104. The control grid of tube .is connected to ground through a resistor 105 and' through a condenser 106 to the anode of tube 101. The control gridof tube 101 is connected to ground through a resistor 107 and through a condenser 108 to the anode of tube 100. The time constants of re'sistancecapacitance units 105, 106 and 107, 108 are so adjusted as to produce a substantially square wave output at the anode of tube 101. The square wave output is ditferentiated by condenser 109 and grounded resistor 110 to produce the pulses 53 and 54, Figure 4. These pulses are rectined by diode 111 to produce the timing pulses 57,'Figure 4. The timing pulses are fed to oscillator 59, Figure 3, through a suitable coupling condenser and to an RC circuit. The simplest form of RC circuit consists of a resistor 112 and a grounded condenser 113 attached to the cathode of diode 111, Figure 5. Condenser 113 is charged by each timing pulse 57 and thereafter slowly discharges through a resistor 113a connected across said condenser to produce the inverted sawtooth wave form 73, Figure 4, across output terminals 114 and 115. v

The inverted sawtooth waves 73 from output terminals 114, 115 are fed to an isolating amplifier, not shown, for impedance matching purposes and, thence, to a stator winding 117, Figure 6, of a rotary transformer 118. The rotor of the transformer-is mechanically connected to receiving syncro 71, and this rotor has two windings 119, connected so that they are electrically 90 degrees out of phase with each other. These windings are connected through slip rings 121 to the respective deiiection plates 122, 123 and 124125 of cathode ray tube 68. Winding 119 produces a voltage which is equal to the product of theinverted sawtooth voltage fed to winding 117 and the sine of the angle of inclination of winding 119 with respect to winding 117. This is the voltage wave 78 of Figure 4. The voltage produced by winding 120 is 90 degrees out of phase with respect to the voltage produced by winding 119, and is frepresented by voltage wave 79 of Figure 4. As previously explained, when these voltages are applied to deflection plates 122, 123 and 124, 125, a circular sweep is produced with a linear radial sweep superimposed thereon to deliect the cathode ray beam cyclically in a substantially linear path between the pattern.

Although, for simplicity, I have shown a very direct way of obtaining the modulated circular sweep voltage, I do not intend that the invention be limited to this method.

center and periphery of the circular sweepv driven by-.ysyncro l'71. to. magnetically. focus.thet.electron. beam.. Al-ternatively,. slowly varying- ,lsne.. and cosine.. v oltages .may be. obtained from .a .sinusoidal..potentiom,. eter fed. by-direct-current,.or..the..sine,and cosine .voltages may beobtained by, modulation :of signalsfrom-analternatingcurrent resolver.` Anyfother methodsfofobtaining, the modulated-1.v circular sweep voltage i which are knownv to--those skilledinthe art mayV be..used,.in the apparatus. oflthe present invention...

4In Figure 7, I have shown.- suitable and ATR switches for. use. in-the apparatus of.. this. invention.' It will, be noted. that-oneoutputterminal of. oscillator 59 is grounded, 4and. the other. terminals. connected .through a..cold.cathode gastube 127 to one4 conductor 128.of. transmission line4 61, .the other. terminal 129wbeing. ground-- ed..A Conductor. 128 is-connectedthrough resistors 130- and..131v to one. input .terminalof amplifier 64, ther-.other input terminal of. whichisgrounded.. The .junction between.. resistors 130, .-131 .is connected,- lto ,ground Lthrough. a.second 4cold .cathode .-gas.-tube..132.

When a pulseis. produced by` oscillator: 59,.gas tube 1274 becomesconductive and. energy4 is transmitted over line 61, very littleenergy. tendinggtoll'ow. through resistance 1304 due to its..relative.,high, impedance-.compared with-the transmissionline 61. and its load-impedance at the remote end.. The energywhichidoes:passthrough resistorv 130 flows to ground .through .the .relatively low. impedance gashtube 132. so that.. only a negligible. amountofthe transmitted energy. passes. through resistor-131. and .theinputcircuitseof amplifier. 64.. However, bothgas tubes 127, 1321--oflrV a relatively. highimpedance to the. low. amplitude signals passing back.` to` the. TR.ATR' unit throughtransmission line. 61.. Accordingly, these signals pass throughfresistors130 and 131:tothe input.crcuitsoffamplifier 64;.. only a-small part of the-signal energy beingdivertedv through the gas-tubes. to ground. ortho. oscillator output-circuit. Thus,.,the `apparatus of Figure 7,v in effect, connects the oscillator 59 to line 61- and ldis connects. amplifier 6.4.- therefrom during. periods. of transmission while, during periods of reception, the apparatus connects amplifier. .64 totransmission line 61 and disconnects oscillator. 59 therefrom.

Although IV have. described. certainspecific circuitsfor performing the functions ofthe units off the block dia-- gram, Figure 3, itwill be understood thatother circuits.7 for. performingthe. same functions. may.: be substituted. therefor without, departing.. from.l the: spiritand scopeof: tlieinvention.

InFigure 9,y I have shown.l a modified scanning device 13,5"which is adapted to. be substitutedfon'scanning.device. 17Figure1.v The device is. shown suspendedina liquid-- containing bore hole- 136 and it. includes.. two parabolic reflectors 137, 138.having elastic-bodes-1'39, 140'mount'- ed at the foci thereof,. respectively,.,inthe manner explained iggconnection 4with Figure 1.v Oil filled; membranes may also be. provided. in the .manner -explainedin connection with Figure 1.. Thereiiectors. are. arranged',l so,l that, when a pulsed ultrasonic. beam is.- radiated from one. elastic. body 139 o1'. 140, the waves. reflected from: the adjoining strata of. interest. are; 4incid-ent uponthe. otlier'elastic body. The waves. reflected from strataA 141-, 142.,and' 143 produce electrical: voltageswhen they reach thev elastic body, and. these voltages- .produce a displayv uponthe screen of the cathode rayftubel whichshows the nature and locationof the. subterranean strata.

'Itwill be noted that the scanner 13S-utilizesA the- Waves; reflected so thatl the angle of incidence equals the angle' of refraction, rather than. the direct reflections, as in Figure 1. Since separate transmitting and receivingunitsare utilized, itis not lnecessary-'to utilize the TR and. ATR switches. 60 and. 63 .of the .block diagram,k Figure 3.v Rather, one elastic. body 139V or 140 isgconnecteddirectly. to the oscillator 59 and the other elastic body is connected. qilly t .theamplier -64- Figure l'I discloses "a `unit. where circular scanninghia notntilized, thus..enablinathenioton16.syncliro 1.91 andgyro 3.6 to be eliminated.. Although 'unit dqe'snot- -allowthe formations` to be locatedazimuth, it ,giyes'inf formation concerning average, character, and distance of the adjoining. formations... This unitv includes two of reflector 149.2.nd an elastic body152 is mounted at the..

focus of reector 150. An oil iilledmembrane may. be secured. tothe peripheral regi-on of eachof lthe reflectors 149,- as describedin connection` with Figure -l. A han rier 153 of a radiation4 absorptive material such as rub,- berv may be interposedy betweenthereectors 149,150 and supported by theposts. 147. to prevent the passage of radiation in a direct path between the reflectors. Due to the fact that the direct path length between transmitterand receiver is considerably shorter than any of-the reection path lengths, the-barrier between transmitter and receiver is not absolutely essential --since they direct radiation` reaches the receiver before therellected radiation, and thereceiver circuits-can befblanked vwhile the-direct radiation isreceived.

When a pulse of radiation isv emitted bygone of the elasf tic bodies 151- or- 152,'.it is reectedfrom the bore hole walls and adjoining formations, after whichltheA reflectedv radiation is incident upon the otherelastic body-'to produce an electrical voltage representative of the average characteristics of the bore hole wallsl and adjoining formations, .as well as-their averagedistance from the elastic bodies 151 and 152. The aforesaidvoltage may be ap: plied directly, after suitableamplification, to control the deflection or intensity of the electron beam ofa cathode raytube. Circular-sweep--of the beam is, of course, unnecessary, since no scanning ofthetransrnittedor received` ultrasonic beam is provided. Accordingly, anordinary sawtooth wave may be applied to the-deflection plates ofl the cathode ray tube to produce-a linear sweep. The p0- sition of the trace produced by the reected wave along the linear swcepline determines the distance of the formation producing the. trace from the vertical axisl connecting elastic bodies 150 and. 151. Alternatively, if desired, the voltages produced by the elastic body at which the waves are received may be fed directly to a conven. tional recording device, s uch as. an oscillographic recorder. v

It may be advantageous inl-.some .cases to derive the linear sweepvoltage for. the cathode ray tube from a po- -tentiometer geared to the cable suspendingthedevice 145, 146v in the bore hole. Such a potentiometer is shown by Figure l2 as including a stationary resistanceelement 156I and a contact arm 157 which.is r-o tate,d as the cable supporting scanner element 145, 146is lowered intothe bore hole. This may be4 effected by mounting afecler wheel in contact. with the cable, thiswheel being gearedto the, shaft carrying contact arm 157. A` potenti-al is applied across terminals.158159,.and-onesetof deflection plates of a cathode ray tube -is connected to potentiometer -terminal 160 and one of the l switch isalso actuated by the shaftcarrying contact armA 157,V thev switch contacts closing when the potentiometer f arm 157 is positioned between terminals 158 and 159. Thisv switch is connected `to a circuit, for pnoducing a trigger voltage to actuate the oscillator which supplies en.- ergy to the elastic body 151 or 152, Figure 1l.

As the cable is lowered into the bore hole, potentiometer arm 157 is continuously rotated. Each time-the arm 157 is positioned: between terminal-vs, 158, 159- the cam switch isv actuated, causing a, pulsed beam of ultrasonicenergy to. be radiatedv fromone, of theelastic bodies .151, 152. As the. potentiometerrotates.betweenpulse, trans,- missionaza constantlyincreasingnvoltage is applied to theterminalslSS, or 159. A can-1V cathode ray-tube deflection plates, causing the electron beam to`sweep in a linear path across the screen. During this linear sweep period, reflectedradiation is incident upon one of the elastic bodies, thus producing a voltage which produces a tra-ce upon the cathode ray tube screen. The position of the trace along the linear sweep line determines the time interval between transmission and reception of the pulse, and hence the distance of the reflecting formation from the radiation source. The nature of the trace is representative of the average character of the formati-on from which 4the radiation is reflected, due to differences in absorption and reflection characteristics of different formations.

The modified form of radiator shown by Figure 13 is similar to that of Figure 1l except that one unit is utilized both for transmission and reception. This unit includes a housing 156 which is suspended in a liquid filled bore hole by a cable 1547. A reflector 158, which is flattened somewhat from a true parabolic shape, has an elastic body 159 suspended at its focus. An oil filled membrane may be secured to the periphery of the reflector, as described in connection with Figure l. When a pulse of radi-o frequency energy is applied to elastic body 159, a fan shaped beam of -ultrasonic radiation is directed downwardly and outwardly against the walls of the bore hole and 'adjoining formati-ons. After the transmission, ultrasonic waves reflected by the formations are converted into electrical voltl ages representative thereof by elastic body 159, and these voltages are indicated or recorded by any of the methods set forth in 4connection with Figure ll. The apparatus differs from that -of Figure 11 in that direct reflections, rather than angular reflections are used.

Figure 14 shows a tandem crystal unit which may be substituted for any of the elastic bodies, such as elastic body 26, Figure l. The unit includes a series of stacked piezoelectric crystals 161, each crystal having one face securely cemented to an electrode 162 and its other face securely cemented to an electrode 163. The electrodes 162 are all connected 4to a common bus bar 164, and the electrodes 163 are all connected to a common bus bar 165. The tandem crystal arrangement is advantageous in that wide band 4frequency response may be provided by using a plurality of crystals having slightly different resonant frequencies. The operating frequency can be selected without removing the instrument from the bore hole simply by choosing the driving radio frequency of the surface instrument.

Figure l `shows a transmitter or receiver unit in which a volume of o-il surrounds the crystal without the necessity of providing a membrane around the oil. This unit includes a reservoir 168 having a tube 169 mounted therein, this tu-be extending upwardly from an inverted cup shaped member 170. An elastic body 171, such as a piezoelectric crystal, is suspended in member 170 by a rod 172. The tube 169 carries the conductors, not shown, connected to the crystal electrodes. Reservoir 168 communicates with cup shaped member 170 through a relief valve 173. In the operation of the unit, oil is slowly forced into member 170 from the reservoir 168 by a pump, not shown. The oil, being lighter than the liquid in the bore hole, oats in the member 170. Any oil which escapes is replaced by oil which is continuously pumped into member 170 at a slow rate from the reservoir. Accordingly, a volume of oil is maintained around the crystal 171 at all times without the necessity of providing a confining member, such as membrane 28, Figure 1.

Figure 16 illustrates an electrical scanning circuit which enables a directional beam to be swept in a circular path around the bore hole formations Without the necessity of providing a scanning motor. In this ligure two mutually perpendicular tiat crystals 176, 177 have their electrodes connected, respectively, to two mutually perpendicular rotor windings 179, 180 of a goniometer 181. The crystals 176, 177 have dimensions which are small compared to' the wavelength of the radiation to be emitted. Radio frequency energy is applied to the stator coil 182 when it is desired to transmit a pulse of ultrasonic energy from the radiator. The goniometer is rotated at the speed at which it is desired to scan the formations adjoining the bore hole. The energy is radiated from the crystals in a highly directional beam which is dependent on the position of the goniometer windings. Thus, an electrical scanning system replaces the mechanical scanning system of Figure 1.

Although the system has been described in connection with present preferred embodiments thereof, the invention is not to be limited thereby, but only by the scope of the appended claims. Thus, although the system has been described in connection with investigating formations adjoining a bore hole, it will be understood that other formations, such as underwater formations, may be investigated by the method and apparatus of this invention. The apparatus is also very useful in drilling operations wherein a transmitter-receiver unit is mounted on or adjacent the drill bit, thereby providing useful information concerning the nature and character of adjoining formations as the drilling progresses.

It will be understood that the sweep generator and multivibrator circuits of Figure 5 may be replaced by more elaborate circuits, if desired. For example, vacuum tube stages may be inserted between the wave shaping units of Figure 5, and a crystal controlled oscillator may be coupled to the multivibrator circuit for synchronization purposes, thereby to obtain a more accurate timing signal. For simplicity, however, I have shown the least involved circuits possible. Further, the TR and ATR switches, Figure 3, may be eliminated unless very high powers are utilized. In such cases, the input circuits of amplifier 64 should be constructed to stand a considerable overload, and such circuits should be able to recover within a few microseconds after the overload is removed.

What is claimed as new Letters Patent is:

1. The method of investigating subterranean formations adjoining a bore hole which comprises transmitting from a fixed position and at a known azimuth angle a pulsed beam of ultrasonic radiation through said bore hole in an inclined path against said adjoining formations, detecting at a fixed position and substantially from said known azimuth angle ultrasonic radiation reflected and scattered from said adjoining formations, the path length of said radiation varying with the depth of said formation from which it is reected, relative to said positions of transmission and detection, and measuring the time interval between the transmission of said pulse and the detection of the individual reflected radiations, thereby to determine the profile of said formations.

2. The method of investigating subterranean formations adjoining a bore hole which comprises transmitting from a fixed vertical position and at known azimuth angles a succession of pulsed lbeams of ultrasonic radiation through said bore hole, displacing the beam in an angular direction so that vsuccessive pulses are directed against c'ircumferentially spaced regions of said adjoining formations, all of which are vertically displaced from the transmlssionpoint, transmitting anglefdata to the surface representative of the azimuth of said beam, detecting ultralsonic radiation reflected and scattered from said adjoinin g formations, the path length of said radiation varying with the depth of the formation from which it is reflected relative to said fixed vertical position measuring the time and desired to be secured by interval between the transmission of each pulse and the detection of its individual refiected radiations, and correlatingsaid time intervals with said angle data, thereby to determine the profile of said formations in distance and azimuth.

3. The methodof investigating subterranean formations adjoining a liquid-containing bore hole as in claim 1-3 1, s aid detectingzposition being vertically spacedv from. said transmitting position. at a distance suchl that the angle of incidence-.of `the transmittedl beams upon said formations is lsubstantially equal to the angle of refraction of the retiected beams fromA s aid formations.

4. The methodl of investigating subterranean formations adjoining a liquid-containing bore hole as in claim 1, said transmitting,v and detecting positions being identically located, said radiation reectedand scattered from said formations being detected during the interval between each pair of successive pulse transmissions.

5. Apparatus for investigating subterranean formations which. comprises,` inv combination, a casing, ay cable for lowering said casing into a bore hole, means for establishing a xed angular position of said casingv in said borehole, a piezoelectric crystal carried by said casing, said crystal being adapted for vibration at ultrasonic frequencies, a transmission line for supplying radio frequency electrical energy to said crystal to elfect. vibration thereof at ultrasonic frequencies, a reilector for focusing ultrasonic radiation produced by said crystal into a beam directed obliquely with respect to the axis of said casing, means for rotating said reector about said axis to scan the formation adjoining the bore hole, and means for establishing the position of said reflector relative' to said casing.

6. Apparatus for investigating subterranean formations comprising, inV combination, a casing, a cable for lowering said casing into a bore hole, a piezoelectric crystal carried by said casing, said crystal being adapted for .vibration at ultrasonic frequencies, a pair of electrodes se- .cured to opposite faces of said crystal, a transmission line for supplying radio frequency energy to said electrodes, thereby to effectyibration of said crystal at ultrasonic frequencies, a parabolic reflector tilted with respect .to the vertical axis of the casing for focusing ultrasonic waves produced by vibration of said crystal into a beam, a motor for rotating said reflector about said vertical axis to scan the formations adjoining 4the bore hole, a transmitter rotated by saidA motor to provide angle data representative of the angular position of said reilector, a gyro wheel mounted in a plane defined by the axis of said casing, and means for rotating said wheel to substantially prevent rotationvof the casing about its vertical axis.

7. Apparatus for investigating subterranean formations which comprise's, in combination, a casing, a cable for loweringl said` casing intol a bore hole, an assembly mounted for rotary movement with respect to saidzcasing, said assembly including a pair'of vertically spaced elastic bodies adapted to vibrate at ultrasonicifrequencies, a parabolic reflector associated with each elastic body,said reflectors being disposed in facing position in a common radial plane and being tilted with respect to the vertical axis of said casing, means for rotating said assembly to scan formations adjoining the borehole, means for substantially preventing rotation of said casing about its vertical axis, means associated with' one of said pair of elastic bodies, including one of said reflectors, for transmitting a-pulsed beam of ultrasonic radiation through said bore hole, means associated with the. se'cond of said' pair of elastic bodies for receiving and `detecting a fraction of said pulsed beam of radiation, and means for measuring the time interval between the transmission of saidy pulsed beam and the reception and detection of said fraction of said pulsed beam o f radiation.

8. Apparatus for investigatingA subterranean formations, as in claim 7,- said means for rotating said assembly to scanl formations adjoining the bore hole comprising a motor, a transmitter rotated by said motor to provide angle data representative of the angular position of said assembly, said means for preventing the rotation of said casing about its fvertical axis including a gyro wheel Vrinountedin a plane defined by the vertical axis of the "casing and a second` transmitter for providing data repre- -14 sentative of thedeviationof" the casing from a .predeterlf mined angular position.

9. Apparatus for investigating' subterranean formations,j as in claim 7 saidpair of elastic bodies comprising piezoelectric crystals.

l0. 'lhe method of. producing a display upon the face of a cathode ray tube whichY comprises detl'ecti'ng the electron beam of a cathode ray tube to produce a circular sweep, and further deecting the electron beam in accordance with an inverse saw tooth wave of substantially higher frequency than the circular sweep frequency, and applying said wave. as a deflection voltage to cause said beam to move rapidly from the center to the periphery of saidv circular sweep as the amplitude ofA said wave rises abruptly to a peak valiie', and to cause said beam to m`ove backslowly from the periphery of said circular sweep to the center as the .amplitude of saidv wave gradually de'- creases from its peak value.

1'1. rthe method of producing a display upon the face of a cathode ray tube' which comprises deflecting the electron beam of a cathode ray tube to produce a circular sweep, generating a square wave' voltage of substantially higher frequency than the sweep frequency, differentiating and rectifying the square wave voltage, integrating the rectilied voltage' to provide a wave yof inverse saw tooth configuration, the amplitude of which, during each cycle, rises abruptly to a peak value and thereafter gradually decreases, and further deflecting said electron beam in accordan'ce with said inverse saw tooth voltage, whereby the electron beam periodically moves abruptly from .center to periphery of the circular sweep area, and then moves slowly Afrom the periphery to the center.

12. The method of producing a display upon the face of a cathode ray tube which comprises deectng the electron beam of a cathode ray tube by applying energy thereto in a plane perpendicular to said' beam, modulating the energy applied in one direction in accordance with a sine function, modulating the energy applied in a perpendicular direction in accordance with a cosine function, there'- by to produce a circular sweep of said electron beam, and superimposing a wave of inverse saw tooth configuration upon the modulating potentials, said wave being of substantially higher frequency than the modulating potentials, and applying said wave as a deection voltage to cause said beam to move rapidly from the center to the periphery of said circular sweep' as the amplitude of said wave rises abruptly to a peak value, and to cause said beam to move back slowly from the periphery of said circular sweep to the cen-teras the amplitude of said wave gradually decreases from its peak value.

13. The method of producing a display upon the face of a' cathode ray tube' which comprises deiiecting the electron beam of a cathode ray tube by applying energy thereto in a plane perpendicular to said beam, modulating the energy applied in one direction in accordance with a sine function, modulating the energy applied in a perpendicular direction in accordance with a .cosine function, thereby to produce a circular sweep of said electron beam, generating a square wave voltage of substantially higher frequency than the sweep frequency, differentiating and rec tifying the square wave'voltage, integrating the rectified voltage to provide a wave' of inverse saw tooth configuration, the amplitude of which, Vduring each cycle, rises abruptly to a peak value and thereafter gradually de# creases, and further deflecting said electron beam in accordance with Said inverse saw toothvoltage, whereby the electron beamy periodically moves abruptly from center' to periphery of the circular sweep area, and then moves slowly from the periphery to the center.

14. The method of investigating subterranean formations adjoining a borehole which comprises deiiecting the electron b'eam of a cathode ray tube to produce a circular sweep, further deecting said electron beam in accordance with amplitude variations of a saw tooth wave, each cycle of 4said wave including a steep wave assaut/i front and a generally linear inclined portion, directing a pulse of ultrasonic radiation against the formations adjoining a bore hole simultaneously with the production of each steep wave front, converting ultrasonic radiation reflected from said formations into electrical voltages representative thereof, and modulating said electron beam with said voltages during each period when said beam is deflected by the inclined portion of a saw tooth wave.

` 15. The method of investigating subterranean formations adjoining a bore hole which comprises transmitting a succession of pulsed beams of ultrasonic radiation through said bore hole aga-inst the adjoining formations. producing -a steep wave front simultaneously with each transmission, displacing said beams in an angular direc\` tion so that successive pulses are directed against cirl5 cumferentially spaced regions of said adjoining formations, producing voltages representative of the sine and cosine, respectively, of the angle of angular displacement of said beams, applying said sine and cosine voltages to the respective sets of deflection plates of a cathode ray tube to' produce a circular sweep, the angular velocity of which is equal to the angular velocity of said radiation beams, converting radiations reliected from the borehole formations into elec-trical voltages representative thereof, producing an inclined wave form during each conversion period, said inclined wave form defining a saw tooth wave with said steep wave front, varying the intensity of the cathode ray tube electron beam in accordance with said reflection voltages, and applying said saw tooth wave to said deflection plates to produce a radial sweep of said electron beam.

16.v A display circuit for ya cathode ray tube comprising, in combination, a cathode ray tube having two sets of mutually perpendicular dellection plates, a generator having a pair of windings 90 degrees out of phase, leads coupling the respective windings to said sets of de-ection plates, a condenser, means for periodically charging said condenser 4to produce a steep wave front, a resistance for discharging said condenser to produce a generally linear portion of decreasing amplitude Iafter each steep wave Ifront, whereby an inverted saw tooth wave is produced, and means for deliecting said electron beam in accordance with said inverted saw tooth voltage to produce a radial sweep.

17. A display circuit for a cathode ray tube comprising, in combination, a cathode ray tube, means for producing a circular sweep of the electron beam of said tube, a multivibrator for producing a succession of square waves, a dierentiating circuit fed by said multivibrator, a rectifier fed by said differentiating circuit to produce a series of sharp unipolar pulses, a condenser, means for applying said pulses to periodically charge said condenser and produce a steep wave front, a resistor to discharge said condenser, thereby producing a generally linear portion of decreasing amplitude after each steep wave front, and means for deflecting said electron beam in accordance with the amplitude of the inverted saw tooth Wave produced by said resistor-condenser unit, thereby to produce a radial sweep.

18. Apparatus for investigating subterranean formations comprising, in combination, an oscillator for producing energy of ultrasonic frequency, a transducing means disposed in said bore hole for converting electric energy into ultrasonic radiation and for converting ultrasonic radiation into electrical energy, means coupling said oscillator to said transducing means, a cathode ray tube, means for detlecting the electron beam of said cathode ray tube to produce a circular sweep, a timing circuit for periodically exciting said transmitter to produce a pulse of ultrasonic radi-ation 4at said transducing means and to simultaneously produce a rapid radial sweep of the cathode ray tube electron beam, a circuit for connecting .said transducing means to an electrode of said cathode ray tube whereby reflected ultrasonic radiation incident :upon said transducing means produces variations in in- 7.5

. 16 tensity of the cathode ray tube electron beam, and means :associated with said timing circuit to gradually decrease the radial sweep voltage during the period of reception of rellected radiation.

19. Apparatus for investigating subterranean formations comprising, in combination, an oscillator for producing energy of ultrasonic frequency, transducingmeans disposed in a bore hole for converting electrical energy into ultrasonic radiation and for converting ultrasonic radiation into electrical voltages representative thereof, means for focusing ultrasonic energy incident upon or radiated from vsaid transducing means, means for rotating said transducing means to sweep the formations adjoining the bore hole, means including a sensing device connected to said rotating means to produce an output representative of its angular position, and a generator controlled by said sensing means for producing a circular sweep of the cathode ray electron beam at the same angular velocity as that of said rotating means, a timing circuit for periodically exciting said -oscillator to produce a pulse of ultrasonic radiation at said transducing means and -to simultaneously produce a rapid radially outward sweep of the cathode ray tube electron beam, a circuit for connecting said transducing means to an electrode of said cathode ray tube whereby reected ultrasonic radiation incident upon said transducing means produces variations in intensity of the cathode ray tube electron beam, and means -associated with said timing circuit to gradually decrease the radial sweep voltage during .the period of reception of reflected radiation.

20. Apparatus for investigating subterranean formations as .in claim 5, an oscillator coupled to said transmission line, a cathode ray tube, means responsive to the lowering of said cable to produce a sweep voltage for said cathode ray tube and to periodically produce trigger signals to excite said oscillator, means coupling said oscillator to said transmission line to produce a pulse of ultrasonic radiation in said bore hole at each excitation of said oscillator, and a circuit for connecting said transmission line to said cathode ray tube whereby reflected ultrasonic radiation incident upon said piezoelectric crystal produces representative traces upon the screen of said cathode ray tube.

21. Apparatus for investigating subterranean formations as in claim 5, an oscillator coupled to said transmission line, a cathode ray tube, a potentiometer coupled to said cable to produce periodic resistance variations responsive to the lowering of said cable into the bore hole, a circuit including said potentiometer for impressing a sweep potential on said cathode ray tube, switching means associ-ated with said potentiometer to produce a trigger signal during each cycle of revolution of said potentiometer and to apply said signal to said oscillator and thereby produce a pulse of radio frequency energy, means coupling said oscillator to said transmission line to produce a pulse of ultrasonic radiation in said bore hole at each excitation of said oscillator, and a circuit for connecting said transmission line to said cathode ray tube whereby reflected ultrasonic radiation incident upon said piezoelectric crystal produces representative traces upon the screen of said cathode ray tube.

22. Apparatus for investigating subterranean formations Which comprises, in combination, a casing, a cable for lowering said casing into a bore hole, an elastic body carried by said casing and being adapted for vibration at ultrasonic frequencies, a transmission line forming a part of sa'id cable for supplying vibratory energy to said elastic body, a reflector for focusing ultrasonic waves produced by vibration of said elastic body, means for substantially preventing angular movement of said casing, a Ifreely suspended gyro wheel mounted on said casing in a plane defined by the vertical axis of said casing, and means responsive to relative rotary movement between said casing and said gyro wheel for producing a signal whose amplitude is proportional to the deviation of the casing .from a predetermined angular position.

23. Apparatus for investigating subterranean formations which comprises, in combination, a casing', a cable for lowering said casing into a bore hole, an elastic body carried by said casing and being adapted for vibration at ultrasonic frequencies, a transmission line forming a part of said cable for supplying vibratory energy to said elastic body, a reflector for focusing ultrasonic waves produced by vibration of said elastic body, means for substantially preventing the rotation of said casing about its vertical axis, means associated with said elastic body, including said reflector, for transmitting a pulsed beam of ultrasonic radiation in an inclined path through said bore hole and against formations adjoining said bore hole, means associated with said elastic body for detecting radiation reected and scattered from said adjoining formations, means for measuring the time interval between the transmission of said pulsed beam and the detection of the reflected and scattered radiations, and means for surrounding said elastic body with a fluid adapted for the transmission of ultrasonic radiation, said fluid being adapted for contact with liquids normally present'in the bore hole.

24. Apparatus for investigating subterranean formations which comprises, in combination, a casing, a cable for lowering said casing into a bore hole, an assembly including a pair of elongated piezoelectric crystals suspended from said casing, said crystals being arranged perpendicularly to each other, and means for applying ultrasonic energy modulated by slowly varying sinusoidal voltages of v opposite phase to the respective crystals to produce a circularly sweeping beam of ultrasonic radiation, the plane of vibration of said assembly being inclined with respect to the axis of said casing, means associated with said assembly to pulse said beam of ultrasonic radiation, means within said assembly, including said crystals, for detecting radiation reflected and scattered from the formations adjoining said bore hole, and means for measuring the time interval between the transmission of said beam of ultrasonic radiation and the detection of said reflected and scattered radiations.

25. Apparatus for investigating subterranean formations comprising, in combination, an oscillator for producing energy of ultrasonic frequency, transducing means disposed in a bore hole for converting ultrasonic radiation into electrical energy and forv converting electrical energy into ultrasonic radiation, means coupling said oscillator to said transducing means, a cathode ray tube, means for producing a circular sweep of the electron beam of said tube, a condenser, means for charging said condenser to produce a steep wave front, said last-mentioned means including a multivibrator for producing a succession of square waves. a differentiating circuit fed by said multivibrator, a rectifier fed by said differentiating circuit to produce a series of sharp, unipolar pulses, and means for feeding said sharp pulses to said condenser, a resistance f or discharging said condenser to produce a generally linear portion of decreasing amplitude after each steep wave front, whereby an inverted saw tooth wave is produced, means for deflecting said electron beam in accordance with said inverted saw tooth wave to produce a radial sweep, means for exciting said oscillator simultaneously with the production of each steep wave front, and means for connecting said transducing means sc as to deflect said electron beam during each generally linear portion of decreasing amplitude.

26. Apparatus for investigating subterranean formations which comprises a transducer assembly, means for lowering said assembly into a bore hole, said assembly including an elastic body adapted to convert electrical energy into ultrasonic waves representative thereof and to convert ultrasonic waves incident thereon into electrical energy representative thereof, a reflector having said elastic body at the focus thereof and constructed to focus ultrasonic waves produced by said elastic body upon a localized region of limited angular extent at the sides of the bore hole, means for rotating said reflector about the longitudinal axis of said assembly to scan the adjoining formations, sensing means connected to said rotating means and producing a signal representative of its angular position a device having an indicator movable along a time scale, means for simultaneously transmitting a pulse of electrical energy to said elastic body and moving said indicator to an index point on said time scale, means operable between pulse transmissions to move said indicator at a uniform rate along said time scale from said index point, means electrically coupling said elastic body to said indicator so that said indicator is responsive to the intensity of ultrasonic waves incident upon said elastic body, and means responsive to said sensing means to rotate the time scale of said indicator and maintain it at an angular position corresponding to that of said rotating means.

27. Apparatus for investigating subterranean formations which comprises a transducer assembly, means for lowering said assembly into a bore hole, said assembly including a first elastic body for converting electrical energy into ultrasonic waves, a second elastic body vertically spaced from said first elastic body to convert ultrasonic waves incident .thereon into electrical energy representative thereof, directional means associated with said first elastic body for directing radiation against a localized region of the formations adjoining said bore hole, directional means associated with said second elastic body for concentrating ultrasonic waves reflected and scattered from said localized region upon said second elastic body, means for rotating both of said directional means about the longitudinal axis of said assembly to scan the adjoining formations, sensing means connected to said rotating means and producing a signal representative of its angular position, a device having an indicator movable along a time scale, means for simultaneously transmitting a pulse of electrical energy to said first elastic body and moving said indicator to an index point on said time scale, means operable between pulse transmissions to move said indicator at a uniform rate along said time scale from said index point, and means electrically coupling said second elastic body to said indicator s o that said indicator is responsive to the intensity of ultrasonic waves incident upon said second elastic body, and means responsive to said sensing means to rotate the time scale of said indicator and maintain it at an angular position corresponding to that of said rotating means.

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